Method and Apparatus for Target Relative Guidance

1. A method of navigating a vehicle comprising an image sensor in the absence of global positioning information, comprising: selecting and tracking a target within an image sequence produced by the imaging sensor; determining a difference between an optic flow due only to motion of the vehicle and the selected target of the image, comprising: determining an effect of motion of the imaging sensor on stationary objects in imaging sensor screen coordinates; determining the optic flow at least in part from a rate of change of the imaging sensor screen coordinates of the stationary objects; and de-rotating the determined optic flow to compute the optic flow due only to translation of the vehicle; determining a vehicle guidance command at least in part according to the difference between the optic flow of the selected target due to motion of the vehicle and the selected target of the image, and an estimate of a ground speed of the vehicle; comprising: determining a heading rate of change command at least in part according to a rate of change in a bank angle of the vehicle, an estimate of an air speed of the vehicle and the estimate of a ground speed of the vehicle; commanding the vehicle and imaging sensor at least in part according to the vehicle guidance command; and determining an imaging sensor pan and tilt command according to the difference between the optic flow of the selected target due to motion of the vehicle and the selected target of the image, and an estimate of the ground speed of the vehicle, comprising: determining an imaging sensor pan and tilt command according to a rate of change in a bank angle of the vehicle, an estimate of the air speed of the vehicle and the estimate of the ground speed of the vehicle; wherein the heading rate of change command and the imaging sensor pan and tilt command are determined according to a control law: ( u ψ u K u λ ) = B - 1 ⁡ ( - Ke - A ⁡ ( V a ϕ . ) ) wherein u ψ represents a commanded vehicle yaw angle rate, u κ represents a commanded imaging sensor pan angle rate, and u λ represents a commanded imaging sensor tilt angle rate, V a represents the vehicle air speed, {dot over (ϕ)} represents the vehicle bank angle rate, B represents an effect of commanded signals on the imaging sensor screen coordinates and a pan angle, and K represents tuned gain parameters.

2. The method of claim 1 , wherein the heading rate of change command is determined according to V ^ g 2 V a ⁢ R d wherein {circumflex over (V)} g is the estimate of the ground speed of the vehicle and R d is a desired orbit radius of the vehicle.

3. The method of claim 2 , wherein the estimate of the ground speed of the vehicle is computed by computing the estimate of the ground speed of the vehicle from the optic flow only due to translation of the vehicle.

4. The method of claim 2 , wherein the estimate of the ground speed of the vehicle is computed by computing the estimate of the ground speed of the vehicle from the estimate of the air speed of the vehicle and a wind estimate.

5. An apparatus for navigating a vehicle comprising an image sensor in the absence of global positioning information, comprising: a processor; a memory, communicatively coupled to the processor, the memory for storing instructions comprising instructions for: determining a difference between an optic flow due only to motion of the vehicle and a user-selected target of an image produced by the imaging sensor, comprising: determining an effect of motion of the imaging sensor on stationary objects in imaging sensor screen coordinates: determining the optic flow at least in part from a rate of change of the imaging sensor screen coordinates of the stationary objects; and de-rotating the determined optic flow to compute the optic flow due only to translation of the vehicle; determining a vehicle guidance command at least in part according to the difference between the optic flow of the selected target due to motion of the vehicle and the selected target of the image, and an estimate of a ground speed of the vehicle, comprising: determining a heading rate of change command at least in part according to a rate of change in a bank angle of the vehicle, an estimate of an air speed of the vehicle and the estimate of a ground speed of the vehicle; commanding the vehicle at least in part according to the vehicle guidance command; and determining an imaging sensor pan and tilt command according to the difference between the optic flow of the selected target due to motion of the vehicle and the selected target of the image, and the estimate of the ground speed of the vehicle, comprising: determining the imaging sensor pan and tilt command according to a rate of change in bank angle of the vehicle, the estimate of the air speed of the vehicle and the estimate of the ground speed of the vehicle; wherein the heading rate of change command and the imaging sensor pan and tilt command are determined according to a control law: ( u ψ u K u λ ) = B - 1 ⁡ ( - Ke - A ⁡ ( V a ϕ . ) ) wherein u ψ represents the commanded vehicle yaw angle rate, u κ represents the commanded imaging sensor pan angle rate, and u λ represents the commanded imaging sensor tilt angle rate, V a represents the estimate of the vehicle air speed, {dot over (ϕ)} represents the vehicle bank angle rate, B represents an effect of commanded signals on the imaging sensor screen coordinates and the pan angle, and K represents design parameters.

6. The apparatus of claim 5 , wherein the heading rate of change command is determined according to V ^ g 2 V a ⁢ R d wherein {circumflex over (V)} g 2 is the estimate of the ground speed of the vehicle and R d is a desired orbit radius of the vehicle.

7. The apparatus of claim 6 , wherein the estimate of the ground speed of the vehicle is computed by computing the estimate of the ground speed of the vehicle from the optic flow only due to translation of the vehicle.

8. The apparatus of claim 6 , wherein the estimate of the ground speed of the vehicle is computed by computing the estimate of the ground speed of the vehicle from the estimate of the air speed of the vehicle and a wind estimate.

9. An apparatus for navigating a vehicle comprising an image sensor in the absence of global positioning information, comprising: means for accepting a selection of a specific target and tracking the specific target within an image sequence produced by the imaging sensor; means for determining a difference between an optic flow due only to motion of the vehicle and the selected target of the image, comprising: means for determining an effect of motion of the imaging sensor on stationary objects in imaging sensor screen coordinates; means for determining the optic flow at least in part from a rate of change of the imaging sensor screen coordinates of the stationary objects; and means for de-rotating the determined optic flow to compute the optic flow due only to translation of the vehicle; means for determining a vehicle guidance command at least in part according to the difference between the optic flow of the selected target due to motion of the vehicle and the selected target of the image, and an estimate of a ground speed of the vehicle, comprising: means for determining a heading rate of change command at least in part according to a rate of change in a bank angle of the vehicle, an estimate of an air speed of the vehicle and the estimate of a ground speed of the vehicle; means for commanding the vehicle and its imaging sensor at least in part according to the vehicle guidance command; and means for determining an imaging sensor pan and tilt command according to the difference between the optic flow of the selected target due to motion of the vehicle and the selected target of the image, and the estimate of the ground speed of the vehicle, comprising: means for determining an imaging sensor pan and tilt command according to a rate of change in a bank angle of the vehicle, the estimate of the air speed of the vehicle and the estimate of a ground speed of the vehicle; wherein the heading rate of change command and the imaging sensor pan and tilt command are determined according to a control law: ( u ϕ u K u λ ) = B - 1 ⁡ ( - K ⁢ ⁢ e - A ⁡ ( V a ϕ ) ) wherein u ψ represents the commanded vehicle yaw angle rate, u κ represents the commanded imaging sensor pan angle rate, and u λ represents the commanded imaging sensor tilt angle rate, V a represents the estimate of the vehicle air speed, {dot over (ϕ)} represents the vehicle bank angle rate, B represents an effect of commanded signals on the imaging sensor screen coordinates and the pan angle, and K represents tuned gain parameters.